What: Approved by the FDA in 2006, this is a matchstick-size rod that is implanted by a doctor under the skin of the upper arm, where it releases a low dose of progestin (etonogestrel). It stays in place, invisible but detectable with a little prodding, for up to three years.
Failure rate*: 0.05%

Who: Women who have just given birth and know they won't remember or have time to return to the doctor for an IUD; women who have grown weary of the pill; women who would rather have something implanted in their arm than their uterus.

Why:

It's impressively effective for three years—which is just slightly longer than the average American family waits to have another baby.

It's safe to use after giving birth, says Carusi.

There's nothing to remember.

Why not:

The implantation is a minor surgery and must take place in a doctor's office.

The idea of having a device under their skin makes some women uncomfortable.